Field
Embodiments of the invention relate to Universal Serial Bus systems. More specifically, embodiments of the invention relate to precision time management in Universal Serial Systems with retimers.
Background
Systems using Universal Serial Bus (USB) are ubiquitous in the modern computing environment. The most recent iteration of the USB follows The Universal Serial Bus 3.1 specification, published Jul. 26, 2013 (USB Spec 3.1) provides for precision time management (PTM), which enables USB devices to maintain a very accurate local clock that is synchronized to a platform master clock. To extend the range of USB, retimers have been defined that re-synchronize and re-drive packets on a link to enable longer trace lines on PCBs and longer cables. Unfortunately, existing retimers introduce highly variable delays in the packets passing through the retimer, rendering PTM unusable for devices in the path of a retimer.